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SCIEXCE-GOSSIP. 



DEXDKITIC SPOTS IX PAPER. 



By F. SfflT-LixGTOX Scales. F.R.M.S. 



TX the first volume of the present series of 

 -L Sctbkce-Gosslp, on page 85. there appeared 

 an article by Mr. A. F. Fair, entitled " Crystals 

 bred in Books." In this Air. Fait dealt with the 

 dendritic spots frequently found in books and 

 papers, one of which he illustrated. Concerning 

 the origin of these spots the author wrote as 

 follows : " Fhe dendritic crystal is formed by 

 chemical action set up by the accidental deposition 

 of a minute fragment of copper upon the surface 

 of paper during the processes of manufacture or 

 of printing : the presence of the minute fragments 

 of copper deposited being probably due to the 

 wear and tear of the paper-making or the printing 

 machinery, so far as the mechanism is built up of 

 copper. The agency of manganese and the action 

 of heat or of moisture in building up the dendritic 



-:al . . . must be left for a future article. The 

 critic crystal requires, as far as I hare observed* 

 rather more than twenty years before reaching its 

 fullest development." On page 268 of the same 

 volume Mr. Carrington observed in connection 

 with the same subject : " Mr. Archibald Liversidge, 

 in ' Journal of Chemical Society ' (vol. x. 1872 

 p. 646), mentions that previous to hi* chemical 

 examination in 1872 dendritic or plumose spots 

 appearing on paper do not seem to have received 

 scientific treatment in view of ascertaining their 

 origin, though botanists and microscopists had 

 frequently examined them without arriving at any 

 satisfactory conclusion. Indeed. Agardh and 

 Lyngbye named the spots Conferva dendritica : 

 and Schumacher placed them amongst fungi 

 under the name Dematinm oliraeeum. Mr. 

 Liversiclge's experiments with the blowpipe, which 

 are set forth at length in his paper now re- 

 ferred to. proved the dendritic spots on paper to 

 be caused by crystals of copper in combination 

 with sulphur." Mr. Carrington, in discussing the 

 sources of origin of other dendrites, further observes 

 that they may in some instances be caused "possibly 

 by cryptogamic vegetable patterns being replaced . 

 -or filled up by the infiltration of some solution 

 containing metal oxide, which crystallises in the 

 cells formed by the vegetation ; for instance in 

 some Mocha stones." Mr. Tait's article called forth 



aal notes by various correspondents, one of 

 whom elaborates the suggestion as to the agency 

 of manganese by saying : " In a small elementary 

 book on minerals, I see that manganese dioxide is 

 employed largely in the manufacture of chloride of 

 lime for the use of linen bleachers ; if so, might 

 not this account for the presence of these beautiful 

 little dendrites on paper, which is so frequently 

 made of old rags ? " Another correspondent says 



he always supposed these dendrites to be " some 

 form of lichen," and another again suggests the 

 manganese origin. 



The subject was therefore one that would 

 well bear further examination, and the present 

 writer, who, as it happens, has a very practical 

 acquaintance with the details of paper-making, 

 accordingly decided to make further investigations. 

 I have unfortunately not read the referred-to paper 

 by Mr. Liversidge, and consequently cannot judge 

 of his reasons for suggesting the agency of sulphur 

 as well as copper, but the knowledge of paper- 

 making above referred to made me consider the 

 theory as inherently improbable. The agency 

 of manganese can be also dismissed for the 

 same reason, for though bleaching-powder is 

 largely used in paper-making, manganese dioxide 

 is not an adulterant of bleaching-powder, its use 

 being confined to the generation of chlorine gas 

 by a mixture of HC1 and MnCv, the gas itself being, 

 in the process referred to, subsequently passed into 

 contiguous chambers and absorbed by slaked lime. 



By the kindness of numerous correspondents of 

 this journal I have been furnished with many 

 specimens of these dendritic spots. For one of 

 these I am indebted to Mr. W. H. Harris, of 

 Cardiff. From this I have made photo-micro- 

 graphs, and they are here reproduced. Fig. 1 

 represents the crystal in its entirety, and fig. 2 a 

 portion of the same at a higher magnification. In 

 both photographs I have endeavoured as far as 

 possible to include the fibres of the paper. In 

 fig 1 the nucleus of the dendrite is very distinct, 

 and this nucleus is characteristic of all such 

 spots without exception. It will further be found 

 that the ramifications of the dendrite correspond 

 exactly to the lie of the fibres, carrying out in a 

 different sense Mr. Carringtous remarks, already 

 alluded to. as to the crystallisation of a metallic 

 oxide in the place occupied by a vegetable pattern. 

 As a matter of fact, the crystallisation, as it slowly 

 formed, has run along the line of least resistance. 

 namely, in the direction of the principal fibres, and 

 preferably those with large, hollow, central canals. 

 This is clearly shown in the original photo- 

 micrograph represented by fig. 2, where two 

 branches can be seen joined by the unfilled 

 remainder of the fibre causing them. The ramifica- 

 tions of the dendrite depend, therefore, entirely 

 upon the fibres of the paper in which it occurs. 



There are many fibres used in paper-making, 

 but white papers in Europe are made almost 

 exclusively from linen, cotton, esparto grass, and 

 wood-pulp, the latter being both chemical and 

 mechanical. The use of wood-pulp is of com- 



